What do you think of this fanfiction? Twilight/HarryPotter crossover - Basically "review" it. Please :)?

Your writing is very good for a 12 year old. However, what you really need is a beta. A beta is someone who is very familiar with the fandom and can help you not only with the grammar and mechanics but also with keeping true to the story. Try Checkmate.com for HP fanfiction.